Stimuli-responsive systems for controlled drug delivery

ABSTRACT

A method of delivering a therapeutic agent by providing a cross-linked polymer encapsulating the therapeutic agent to a site in a patient. The degradation rate of the cross-linked polymer is correlated with a local concentration of an indicator, and the therapeutic agent is released as the cross-linked polymer degrades.

This application claims the priority of U.S. Provisional Application No.60/434,076, filed Dec. 17, 2002, the entire contents of which areincorporated herein by reference.

This invention was made with government support under Grant Number CTS-0118705, awarded by The National Science Foundation (“NSF”). Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

This invention pertains to a drug delivery apparatus and method and,more specifically, to a drug delivery apparatus and method in which therate of drug delivery is determined through a feedback mechanism.

BACKGROUND OF THE INVENTION

Metabolic diseases such as diabetes affect the lives of millions ofpeople. Many of these diseases may be controlled by administration of aparticular enzyme, hormone, or other agent. Some of these agents can beingested as pills or syrups. Others, such as insulin, must be injecteddaily or even more frequently. Diseases such as diabetes also requireconstant monitoring of the blood levels of certain molecules. Forexample, diabetes patients must give themselves multiple finger pricksevery day to monitor their glucose levels.

Administration of pills or injected insulin may result in uneven bloodconcentrations of insulin or other agents over the course of a day. Forexample, most pills result in a spike in blood concentrations of a drug.These concentrations decrease over time to levels that are nottherapeutically effective. In addition, it takes time for agentsadministered as a pill or even an injection to circulate throughout thebody. However, the appropriate levels of metabolic agents or hormoneschanges over time. Thus, while the average serum levels may beappropriate for the patient, the instant serum concentration of the drugis not optimal at any specific time. As a result, it is desirable tohave a drug delivery method that provides a therapeutic agent in thequantities and at the times required by a particular patient.

SUMMARY OF THE INVENTION

In one aspect, the invention is a material for delivery of a therapeuticagent. The material includes a biodegradable polymer functionalized withan indicator analog and a cross-linking agent that cross-links thepolymer by interacting with two or more indicator analogs. Thetherapeutic agent is contained within the polymer. The degradation rateof the polymer depends on the local concentration of the indicator whoseanalog the polymer is functionalized with, and the material is adaptedand constructed to release the therapeutic agent by degrading.

In another aspect, the invention is a method of producing a deliveryvehicle for a therapeutic agent. The method includes the steps offorming a reverse microemulsion by adding an aqueous solution to amixture of a hydrophobic liquid and a surfactant and agitating themixture. The aqueous solution includes a biodegradable polymerfunctionalized with an indicator analog, a cross-linking agent thatcross-links the polymer by interacting with two or more indicatoranalogs, and the therapeutic agent. The method further includes causingthe cross-linking agent to interact with the polymer to form across-linked hydrogel retaining the therapeutic agent therein andseparating the hydrogel particles from the remaining components of thereverse microemulsion.

DEFINITIONS

“Biomolecules”: The term “biomolecules”, as used herein, refers tomolecules (e.g., proteins, amino acids, peptides, polynucleotides,nucleotides, carbohydrates, sugars, lipids, nucleoproteins,glycoproteins, lipoproteins, steroids, etc.) whether naturally-occurringor artificially created (e.g., by synthetic or recombinant methods) thatare commonly found in cells and tissues. Specific classes ofbiomolecules include, but are not limited to, enzymes, receptors,neurotransmitters, hormones, cytokines, cell response modifiers such asgrowth factors and chemotactic factors, antibodies, vaccines, haptens,toxins, interferons, ribozymes, anti-sense agents, plasmids, DNA, andRNA.

“Biocompatible”: The term “biocompatible”, as used herein is intended todescribe materials that do not elicit an undesirable detrimentalresponse in vivo.

“Biodegradable”: As used herein, “biodegradable” polymers are polymersthat degrade fully (i.e., down to monomeric species) under physiologicalor endosomal conditions. In some embodiments, the polymers and polymerbiodegradation byproducts are biocompatible. Biodegradable polymers arenot necessarily hydrolytically degradable and may require enzymaticaction to fully degrade.

“Growth Factors”: As used herein, “growth factors” are chemicals thatregulate cellular metabolic processes, including but not limited todifferentiation, proliferation, synthesis of various cellular products,and other metabolic activities. Growth factors may include severalfamilies of chemicals, including but not limited to cytokines,eicosanoids, and differentiation factors.

“Polysaccharide”, “carbohydrate” or “oligosaccharide”: The terms“polysaccharide”, “carbohydrate”, or “oligosaccharide” refer to apolymer of sugars. The terms “polysaccharide”, “carbohydrate”, and“oligosaccharide”, may be used interchangeably. Typically, apolysaccharide comprises at least three sugars. The polymer may includenatural sugars (e.g., glucose, fructose, galactose, mannose, arabinose,ribose, and xylose) and/or modified sugars (e.g., 2′-fluororibose,2′-deoxyribose, and hexose).

“Small molecule”: As used herein, the term “small molecule” is used torefer to molecules, whether naturally-occurring or artificially created(e.g., via chemical synthesis), that have a relatively low molecularweight. Typically, small molecules are monomeric and have a molecularweight of less than about 1500 g/mol. Preferred small molecules arebiologically active in that they produce a local or systemic effect inanimals, preferably mammals, more preferably humans. In certainpreferred embodiments, the small molecule is a drug. Preferably, thoughnot necessarily, the drug is one that has already been deemed safe andeffective for use by the appropriate governmental agency or body. Forexample, drugs for human use listed by the FDA under 21 C.F.R. §§ 330.5,331 through 361, and 440 through 460; drugs for veterinary use listed bythe FDA under 21 C.F.R. §§ 500 through 589, incorporated herein byreference, are all considered acceptable for use in accordance with thepresent invention.

“Bioactive agents”: As used herein, “bioactive agents” is used to referto compounds or entities that alter, inhibit, activate, or otherwiseaffect biological or chemical events. For example, bioactive agents mayinclude, but are not limited to, anti-AIDS substances, anti-cancersubstances, antibiotics, immunosuppressants, anti-viral substances,enzyme inhibitors, neurotoxins, opioids, hypnotics, anti-histamines,lubricants, tranquilizers, anti-convulsants, muscle relaxants andanti-Parkinson substances, anti-spasmodics and muscle contractantsincluding channel blockers, miotics and anti-cholinergics, anti-glaucomacompounds, anti-parasite and/or anti-protozoal compounds, modulators ofcell-extracellular matrix interactions including cell growth inhibitorsand anti-adhesion molecules, vasodilating agents, inhibitors of DNA, RNAor protein synthesis, anti-hypertensives, analgesics, anti-pyretics,steroidal and non-steroidal anti-inflammatory agents, anti-angiogenicfactors, anti-secretory factors, anticoagulants and/or anti-thromboticagents, local anesthetics, ophthalmics, prostaglandins,anti-depressants, anti-psychotic substances, anti-emetics, and imagingagents. In certain embodiments, the bioactive agent is a drug.

A more complete listing of bioactive agents and specific drugs suitablefor use in the present invention may be found in “PharmaceuticalSubstances: Syntheses, Patents, Applications” by Axel Kleemann andJurgen Engel, Thieme Medical Publishing, 1999; the “Merck Index: AnEncyclopedia of Chemicals, Drugs, and Biologicals”, edited by SusanBudavari et al., CRC Press, 1996, and the United StatesPharmacopeia-25/National Formulary-20, published by the United StatesPharmcopeial Convention, Inc., Rockville Md., 2001, all of which areincorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described with reference to the several figures of thedrawing, in which,

FIG. 1A is a schematic of a mechanism of degradation of a cross-linkedpolymer according to an embodiment of the invention.

FIG. 1B is a schematic of an alternative mechanism of degradation of across-linked polymer according to an embodiment of the invention.

FIG. 1C is a schematic of a cross-linked polymer according to analternative embodiment of the invention.

FIG. 2 is schematic diagram of a reverse microemulsion for use withtechniques provided by the invention.

FIG. 3 is a schematic illustrating the release of a therapeutic agentaccording to an embodiment of the invention.

FIG. 4 is a graph of gel cross-linking efficiency vs. Con A/dextranratio at a constant [Con A]=50 mg/ml (dextran molecular weight: 70 K(diamond), 170K (square), 280K (triangle) and 500K (circle)).

FIG. 5 is a graph showing room-temperature gel dissolution pH 7.0 BESbuffered saline solution at [glucose]=50 mg/dl (diamond), 100 mg/dl(square), and 400 mg/dl (triangle) (dextran MW=70K, Con A/dextran=6.1(w/w)).

FIG. 6 is a graph showing room-temperature gel dissolution pH 7.0 BESbuffered saline solution at [glucose]=50 mg/dl (diamond), 100 mg/dl(square), and 400 mg/dl (triangle) (dextran MW=500K, Con A/dextran=6.1(w/w)).

FIG. 7 is a graph illustrating gel dissolution at 37° C. pH 7.0 BESbuffered saline solution at [glucose]=50 mg/dl (diamond), 100 mg/dl(square), and 400 mg/dl (triangle) (dextran MW=500K, Con A/dextran=6.1(w/w)).

FIG. 8 is a schematic diagram of a flow cell constructed to determineintrinsic glucose sensitivity and perform glucose cycling studies.

FIG. 9 is a graph describing the room-temperature intrinsic glucosesensitivity (IGS) curve obtained from a flow cell such as the one inFIG. 8 with a glucose ramp rate of 8.3 mg/dl/min and a gel with ConA/dextran=6.10 (w/w).

FIG. 10 is a graph illustrating the results of room-temperature glucosecycling studies obtained with the flow cell of FIG. 8 with[glucose]_(A)=50 mg/dl and [glucose]_(B)=(A) 250 mg/dl or (B) 500 mg/dland Con A/dextran=6.1 (w/w).

FIG. 11A illustrates room-temperature glucose cycling studies obtainedwith the flow cell of FIG. 8 and a gel of cross-linked mannosylateddextran.

FIGS. 11B-C are graphs illustrating the variation in the stepwisedissolution of ConA/Dextran gels containing various amounts of ManDex at(B) room temperature and (C) 37° C. ([ConA]=50 mg/ml, ConA/Dextran=3:1(w/w), fraction of ManDex=0 (diamond), 0.1 (square), 0.5 (triangle), 0.9(circle), 1.0 (asterisk)).

FIG. 12 includes graphs of (A) insulin release and (B) room-temperaturegel dissolution in pH 7.0 BES buffered saline solution at [glucose]=50mg/dl (diamond), 100 mg/dl (square), and 400 mg/dl (triangle).

FIG. 12C is a graph depicting the room temperature insulin release overtime from methacrylated dextran nanoparticles (0.99 mol methacrylate/moldextran subunit, MW=40K) at glucose concentrations of 100 mg/dl(diamond), 1000 mg/ml (square), and 10,000 mg/ml (triangle).

FIGS. 13A-B are environmental scanning electron micrographs offreeze-dried gel (Con A/dextran=6.1 (w/w), dextran MW=70K).

FIG. 14 is a graph illustrating room-temperature dextran-insulin releaseat [glucose]=50 mg/dl. (diamond), 100 mg/dl (square), and 400 mg/dl(triangle).

FIG. 15A is a ternary phase diagram for a mixture of 3:2 w/w Tween80/Span 80 and 3:1 w/w Captext 355/Capmul MCM with water.

FIGS. 15B-D illustrate dynamic light scattering (DLS) results for selectpseudoternary compositions as a function of water volume fraction(Φ_(A)) at (A) constant surfactant volume fraction (Φ_(S)=0.25) and (B)constant oil volume fraction (Φ_(O)=0.65), and (C) as a function ofsurfactant volume fraction (Φ_(S)) at constant water volume fraction(Φ_(A)=0.10)

FIG. 16 is a series of ternary phase diagrams illustrating the effect oftemperature on reverse microemulsion formation for the mixture describedin FIG. 15.

FIG. 17 illustrates dynamic light scattering (DLS) measurements onreverse micoremulsions containing various aqueous concentrations of (A)Con A (B) insulin (aqueous phase: (square) pH 7.0 BES buffered ceilingand (triangle) 0.1 N HCl).

FIG. 18 is a series of ternary phase diagrams illustrating theconcentration dependent of dissolved insulin on reverse microemulsionphase behavior ([insulin]_(aq)=(A) 20, (B) 10, and (C) 5 mg/ml).

FIG. 19 is a series of ternary phase diagrams illustrating theconcentration dependents of dissolved Con A on reverse microemulsionphase behavior ([Con A]_(aq)=(A) 50, (B) 25, and (C) 12.5 mg/ml).

FIG. 20 is a set of graphs illustrating the effect of (A) Con A and (B)insulin concentrations in the aqueous phase on the RM droplet size for(square) Captex 355, (diamond) Myvacet, and (circle) soybean oilsystems.

FIGS. 21A-B are sets of ternary phase diagrams illustrating the effectof increasing concentrations of dissolved dextrans on reversemicroemulsion formation for molecular weights of (A) 10K and (B) 70K.

FIG. 21C is a graph illustrating the variation of reverse microemulsiondroplet diameter with dextran concentration for varying molecularweights of dextran.

FIG. 21D is a graph illustrating the variation of reverse microemulsiondiameter with dextran molecular weight for varying concentrations ofdextran.

FIG. 22 is a ESEM micrograph of RM-synthesized nanoparticles.

FIG. 23 is a graph illustrating nanoparticle crosslinking efficiency asthe amount of dextran encapsulated vs. the amount loaded into the RMaqueous phase (square: Dex MW=40K, square: ManDex MW=40K, triangle:DexMW=280K, circle: ManDex MW=280K).

FIG. 24 is a graph illustrating nanoparticle crosslinking efficiencyplotted as the amount of Dextran encapsulated vs. the amount loaded intothe RM aqueous phase at a constant (A) [Con A]_(aq)=25 mg/ml and (B)12.5 mg/ml (diamond: MW=40K, square: ManDex MW=40K, triangle: DexMW=280K).

FIG. 25 is a series of graphs illustrating step-wise nanoparticledissolution in pH 7.0 BES buffered saline solution to determineintrinsic glucose sensitivity for (A) dex MW=280K (B) ManDex MW=280K forCon A/dextran=1.6 (triangle), 3.1 (square), 6.2 (diamond) (w/w).

FIG. 26 is a sugar-responsive particle dissolution surface for particlessynthesized in 0.100 ml aqueous phase dispersed in 1.9 g of oil andsurfactants (FITC-dex MW=42K and [A]_(aq)=50 mg/ml).

FIG. 27A is a schematic illustrating the interaction of dextran and ConA given an excess of Con A.

FIG. 27B is a schematic illustrating the interaction of dextran and ConA given an excess of dextran.

FIG. 28 is a graph illustrating room-temperature nanoparticledissolution in pH 7.0 BES buffered saline solution at [glucose]=0 mg/dl(diamond), 100 mg/dl (square), and 1000 mg/dl (triangle).

FIG. 29 is a graph illustrating room-temperature nanoparticledissolution in pH 7.0 BES buffered saline solution at[glucose]=(diamond) 0 mg/dl, (square) 100 mg/dl, and (triangle) 1000mg/dl.

FIG. 30 is a graph illustrating glucose-responsive insulin release fromparticles prepared from FITC-Dex-42 with [Con A]_(aq)=50 mg/ml and[FITC-dex]aq=(triangle) 32 mg/ml, (square) 64 mg/ml, (diamond) 128mg/ml.

FIG. 31 is a graph illustrating the correlation between an amount ofinsulin released at the highest glucose concentration (e.g., insulinencapsulation) and the amount of FITC-Dex crosslinked for each specificformulation.

FIG. 32 is a graph illustrating the variation of blood glucose with timein STZ-induced diabetic Sprague-Dawley rats given a dose of gelconstructed from ConA (50 mg/ml) and dextran-insulin MW 70K (20 g/ml)(diamond) or saline solution (square).

FIG. 33 is a graph illustrating the variation of blood glucose with timein STZ-induced diabetic Sprague-Dawley rats given a single dose(diamond) or a triple dose (square) of gel constructed from ConA (50mg/ml) and dextran-insulin MW 70K (20 g/ml).

FIG. 34 is a graph illustrating the variation of blood glucose with timein STZ-induced diabetic Sprague-Dawley rats given a dose of double doseof gel constructed from ConA (50 mg/ml) and dextran-insulin MW 70K (20g/ml) (diamond) or saline solution (square) after fasting for 6 hours.

FIG. 35 is a graph illustrating the variation of blood glucose with timein STZ-induced diabetic Sprague-Dawley rats given a dose of double doseof gel constructed from ConA (50 mg/ml) and dextran-insulin MW 70K (20g/ml) (diamond) or saline solution (square) during a glucose tolerancetest.

FIG. 36 is a table adapted from Looger, et al. Nature, 423, 185-190(2003) illustrating the modifications to wild type binding proteins forribose (RBP), glucose (GBP), arabinose (ABP), histidine (HBP), andglutamine (QBP) to create binding sites for L-lactate.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

In one embodiment, the invention is a material for delivery of atherapeutic agent. The therapeutic agent may be a bioactive agent, smallmolecule, or biomolecule. The material includes a biodegradable polymerfunctionalized with an indicator analog and a cross-linking agent thatcross-links the biodegradable polymer by interacting with two or moreindicator analogs. The therapeutic agent is contained within thecross-linked polymer. The degradation rate of the cross-linked polymerdepends on the local concentration of the indicator whose analog thebiodegradable polymer is functionalized with, and the material isadapted and constructed to release the therapeutic agent by degrading.

In another embodiment, the invention is a method of producing a deliveryvehicle for a therapeutic agent. The method includes the steps offorming a reverse microemulsion by adding an aqueous solution to amixture of a hydrophobic liquid and a surfactant and agitating themixture. The aqueous solution includes a biodegradable polymerfunctionalized with an indicator analog, a cross-linking agent thatcross-links the polymer by interacting with two or more indicatoranalogs, and the therapeutic agent. The method further includes causingthe cross-linking agent to interact with the biodegradable polymer toform a cross-linked hydrogel retaining the therapeutic agent therein andseparating the hydrogel particles from the remaining components of thereverse microemulsion.

In still another embodiment, the invention provides a cross-linkedpolymer whose degradation rate is determined by environmental levels ofa particular indicator. That is, as the local concentration of theindicator increases, the degradation rate of the cross-linked polymerincreases, and vice versa. While cross-linked, the cross-linked polymerencapsulates a particular therapeutic agent, which agent is released asthe cross-linked polymer degrades. Thus, the release rate of thetherapeutic agent increases as the increased level of the indicatorcauses the cross-linked polymer to degrade more quickly. Once the localconcentration of the indicator decreases, degradation slows. Thetherapeutic agent may be encapsulated by the cross-linked polymer. Forexample, the cross-linked polymer may be formed as a hydrogel havingpores that are too small to allow diffusion of the therapeutic agent outof the cross-linked polymer before it degrades. Alternatively, thetherapeutic agent may be covalently or non-covalently linked to thepolymer. The polymer is cross-linked by the interaction of indicatoranalogs and cross-link receptors in the polymer. As used herein, theterm “indicator analog” indicates a chemical group that interacts with across-link receptor in the same manner as the corresponding indicator.

One skilled in the art will recognize that the indicator analog may haveessentially the same composition as the indicator itself or may be achemically related species. Where the affinity of the cross-linkreceptor for the indicator and the indicator analog are different, thedensity of cross-links should be modified so the desired amount of thetherapeutic agent is released for a given local concentration ofindicator. The indicator analog may be incorporated into the polymerchain during polymerization as part of the backbone or as a side group.For example, the polymer chain may be functionalized with the indicatoranalog. Alternatively, a polymer chain may be derivatized with theindicator analog post-polymerization so that the indicator analog is aspecies linked to the polymer chain through its backbone or side groups,if any.

In one embodiment, the polymer is cross-linked by a polyfunctionalcross-linking agent including cross-link receptors (FIG. 1, anchored“v”) that reversibly interact with the indicator analogs on the polymerchain. As the local concentration of the indicator (diamond) increases,it competes with the indicator analog (anchored diamond) to interactwith the cross-linking receptor, eventually detaching the polyfunctionalcross-linking agent from the polymer and de-cross-linking the polymer(FIG. 1A). One skilled in the art will recognize that the indicatoranalog may be part of the polyfunctional molecule and that thecross-link receptors may be incorporated into the polymer chain in thesame manner as described above for the indicator analog (FIG. 1B).

The polyfunctional molecule may be covalently linked to the polymerchain while still cross-linking the polymer through one or morenon-covalent interactions between the indicator analogs and thecross-link receptors (FIG. 1C). Non-covalent interactions may includeligand-receptor interactions, chemical adsorption, electrostaticinteractions, ionic bonding, hydrogen bonding, van der Waalsinteractions, hydrophobic interactions, dipole-dipole interactions. Avariety of ligand-receptor interactions may be exploited for use withthe invention. For example, the cross-link receptor may interact withthe indicator analog through an antibody-antigen interaction. In oneembodiment, the cross-link receptor is either the antibody or theantigen, and the indicator analog includes the other. Biotin andstrepavadin may be exploited in the same manner. Other ligand-receptorpairs that may be exploited for use with the invention include, but arenot limited to, folate/folate binding protein and iron/lactoferrin.

The techniques of the invention may be exploited to manipulate feedbackmechanisms. In one embodiment, a patient outcome is traced to an excessof a particular substance. A receptor for that substance is adapted foruse as a cross-link receptor. For example, the receptor may simply beattached to a biodegradable polymer to form a cross-linking agent. Apolymer including the characteristic chemical groups of the substance isselected for use as an indicator analog, or the substance itself isattached to a biodegradable polymer. The polymer including the indicatoranalog is cross-linked with the cross-linking agent in the presence of atherapeutic agent that causes a reduction in the level of the substancein the patient. For example, blood glucose levels may be used to controlthe release of insulin from a drug delivery vehicle formed bycross-linking a polysaccharide (the indicator analog for glucose) with alectin, which typically binds glucose and other sugars. Other moleculesthat act to lower blood glucose levels by stimulating insulin secretionin Type 2 diabetics include but are not limited to sulfonylureas,glucagon-like peptide-1 (GLP-1), and GLP-1 analogues such as exanitide,obtained from the Gila monster.

In a second embodiment, the indicator analog and the cross-link receptorare not related metabolically to the function of the therapeutic agent.That is, the cross-linked polymer degrades in the presence of theindicator to release a therapeutic agent with a different function. Forexample, the techniques provided by the invention may be used to providelong-term, mealtime dosing of bioactive agents such as antibiotics andanticancer drugs. Agents to lower lipid levels, for example, lovastatin,attorvastatin, or simvastatin, or triglyceride levels, for example,gemfibrozil, may also be encapsulated using the teachings of theinvention and released at mealtimes. To deliver a biomolecule, bioactiveagent or small molecule using mealtime dosing, it need simply besubstituted for insulin in a glucose-responsive drug delivery device.The increase in serum glucose causes the cross-linked polymer todegrade, releasing the therapeutic agent without significantly changingthe local glucose concentration.

Suitable biodegradable polymers for use in the practice of the inventionare well known in the art and include poly(lactic acid) (PLA),poly(glycolic acid) (PGA) and PLA-PGA co-polymers (PLGA). Additionalbiodegradable materials include poly(anhydrides), poly(hydroxy acids),poly(ortho esters), poly(propylfumerates), poly(caprolactones),polyamides, polyamino acids, polyacetals, biodegradablepolycyanoacrylates, biodegradable polyurethanes and polysaccharides.Natural polymers including alginate, collagen-glycosaminoglycan,collagen, dextran, pullulan, mannan, and chitosan may also be exploitedfor use with the invention.

Polymers including various pendant groups may also be employed. Suchpendant groups may be used to attach therapeutic agents, cross-linkreceptors, or indicator analogs to the polymers. For example, polymershaving —COOH pendant groups (carboxyl bearing polymers, or CBPs) may beused with the invention. Such polymers may naturally include carboxylgroups or may be modified to include them. Exemplary CBPs include butare not limited to carboxylated polysaccharides (CPS) such as alginate(Ag), carboxymethylated-D-manno-D-glucan (CMMG, available from DaiichiPharmaceutical Co.), carboxymethyldextran (CMDex), carboxymethylchitin(CMCh, available from Katakura Chikkalin Co.), N-desulfated N-acetylatedheparin (DSH), and hyaluronic acid (HA). DSH and CMDex may besynthesized according to Sugahara, et al., Biol. Pharm. Bull., 24,535-543 (2001) (see examples). In general, hydroxylated polymers may becarboxylated through reaction with chloroacetic acid under basicconditions. The degree of COOH substitution with respect to monomer mayvary between 1 and 100 mol %. Naturally occuring carboxylated polymersinclude but are not limited to carboxylated poly (amino acids) (CPAA)such as poly-L-glutamate and poly-L-aspartate. The carboxylate contentmay be varied between 1 and 100% mol COOH/mol AA residue bycopolymerizing carboxylated amino acids (e.g., amino acids with acarboxyl group in addition to the carboxyl group which becomes part ofthe polymer backbone) with non-carboxylated amino acids (e.g., aminoacids whose only carboxyl group becomes part of the polymer backbone).

In another embodiment, polymers having —NH₂ pendant groups (—NH₂ bearingpolymers, or NBP) may be used with the invention. Such polymers may benaturally occurring or may be chemically modified to include a primaryamine. The latter include but are not limited to —NH₂ pendantpolysaccharides (NPS) such as deacetylated chitosan (Ch) (Sigma Aldrich,Milwaukee, Wis.) and diethylaminoethyl ether dextran (DEAEDex), MW500,000 g/mol (Polysciences, Warrington, Pa.). The degree of —NH₂substitution with respect to monomer may vary between 1 and 100 mol %.Naturally occuring aminated polymers include but are not limited topoly(amino acids) such as poly-L-lysine (PLL) and its enantiomer. Theamine content may be varied between 1 and 100% mol NH₂/mol AA residue bycopolymerizing an aminated amino acid (e.g., an amino acid with an aminein addition to the amine group that eventually becomes part of thepolymer backbone) with non-aminated amino acids (e.g., an amino acidwhose only amine is that which eventually becomes part of the polymerbackbone). Proteins including epsilon-NH₂ lysine groups (and whichnaturally have alpha-NH₂ terminal groups) may also be used with theinvention.

In another embodiment, polymers having —OH pendant groups (—OH bearingpolymers, or OBP) may be used with the invention. Such polymers may benaturaly hydroxylated or may be chemically modified using standardorganic chemistry techniques to include a hydroxyl group. In addition todextran, naturally occurring OBP include but are not limited topolysaccharides such as yeast mannan (Mn), pullulan (Pl), amylose (Am),amylopectin (AmP), glycogen (Gl), cellulose (Cl), hyaluronate (Hy),chondroitin (ChD), and dextrin (Dx), all of which may be obtainedcommercially from Sigma Aldrich. In addition, poly (amino acids) such aspoly(serine), poly(threonine), poly(tyrosine), andpoly(4-hydroxyproline) may also be employed as hydroxylated polymers.The hydroxyl content of the poly(amino acids) may be varied between 1and 100% mol —OH/mol AA residue by co-polymerizing hydroxylated aminoacids with non-hydroxylated amino acids. Of course, carboxyl, amino, andhydroxyl pendant groups may be mixed in a single polymer byco-polymerizing the appropriate amino acids in desired ratios.

Co-polymers, mixtures, and adducts of the above polymers may also beused in the practice of the invention. Indeed, such combinations may beparticularly useful for optimizing the mechanical and chemicalproperties of the matrix. Both the choice of polymer and the ratio ofpolymers in a co-polymer may be adjusted to optimize the stiffness ofthe matrix and the degradation rate of both the cross-linked polymer andthe component biodegradable polymer.

Exemplary polyfunctional molecules for use as cross-linking agentsinclude plant lectins, or phytohemoagglutinins (PHAs), such asconcanavalin A (Con A) and those derived from pisum sativum (pea),lathyrus odoratus (sweet pea), lens culinaris (lentil), narcissuspseudonarcissus (daffodil), vicia faba (fava bean), and vicia sativa(garden vetch) as well as human analogues such as human mannan bindingprotein (MBP, also called mannan binding lectin, Sheriff, et al.,Structural Biology, 1, 789-794 (1994); Dumestre-Perard, et al.,Molecular Immunology, 39, 465-473 (2002)), human pulmonary surfactantprotein A (SP-A, Allen, et al., Infection and Immunity, 67, 4563-4569(1999)), human pulmonary surfactant protein D (SP-D, Persson, et al.,The Journal of Biological Chemistry, 265, 5755-5760 (1990)), CL-43 (ahuman serum protein), and conglutinin. One skilled in the art willrecognize that any polyfunctional binding protein may be exploited foruse with the invention.

Other polyfunctional molecules may be constructed by chemically linkingmultiple monofunctional binding proteins, for example, antibodies, cellmembrane receptors, and enzymes. Still other polyfunctional moleculesmay be constructed by chemically linking specific binding fragments ofproteins, for example, antibodies, cell membrane receptors, lectins,collectins, and enzymes. Exemplary protein fragments include truncatedMBP (Eda, et al., Biosci. Biotechnol. Biochem., 62, 1326-1331 (1998)),truncated conglutinin (S. Eda, et al. Biochem. J. 316, 43 (1996)),truncated SP-D (S. Eda, et al. Biochem. J. 323, 393 (1997)), and theglucose/galactose binding protein of E. Coli (Salins, et al., AnalyticalBiochemistry, 294, 19-26 (2001)). In addition, a variety of monovalentligand-binding proteins are available commercially from Sigma-Aldrich,including folate-binding protein, thyroxine-binding globulin, andlactoferrin.

Monofunctional molecules and fragments may be linked directly to oneanother or to polymer scaffolds. Suitable scaffold materials include butare not limited to the CBP's, NBP's, and OBP's described above. Proteinsmay be attached to these polymers using the insulin-conjugationprocedures described below. In general, the pendant groups on CBP, NBP,and OBP may be used to attach a variety of indicator analogs orcross-link receptors using standard organic chemistry reactions (seeMarch, “Advanced Organic Chemistry”, 5th ed. John Wiley and Sons, NewYork, N.Y., 2001, incorporated herein by reference) to formpolyfunctional cross-linking agents.

For example, iron-dextran may be purchased commercially fromSigma-Aldrich and condensed with polyfunctional lactoferrin toencapsulate deferoxamine, which may be used in treating iron overloaddisorders. Thyroxine-NH₂ may be conjugated to OBP's using the CNBrsynthesis described in Example 18. Thyroxine-NBP is then condensed withpolyfunctional thyroxine-binding globulin to produce athyroxine-responsive delivery system for treating thyroid disorders. Forexample, methimazole and propylthiouracil may be encapsulated in athyroxine-responsive delivery system to treat hyperthyroidism. Inaddition, folate may be bound to NBP's using carbodiimide coupling asdescribed above for CBPs and sugar. Folate-NBP is then condensed withpolyfunctional folate-binding protein to produce a folate-responsivedelivery system.

Any of these cross-linking agents may be chemically modified withshort-chain polymers, for example, polyethyleneglycol (PEG), to reducein vivo immunogenic response. Activatyed PEG₂, or2,4-Bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine issynthesized according to K. Ono, et al., J. Biomater. Sci. Polymer Edn.2, 61 (1991). Briefly, 110 mg of monomethoxypolyethylene glycol isdissolved in 500 ml of anhydrous benzene. The solution is refluxed at80° C. in the presence of 25 g of molecular sieves 4 A (powder) for 6 h.After cooling, 50 g of zinc oxide and 1.85 g of cyanuric chloride areadded at room temperature. After refluxing at 80° C. for 53 h, theresulting mixture is cooled to room temperature, diluted with 500 ml ofbenzene and filtered. The filtrate is evaporated to dryness underreduced pressure to give activated PEG₂.

PEGylation may be performed according to T. Ueno, et al., J. Biomater.Sci. Polymer Edn. 7, 753 (1996). To 0.4 ml of protein (2.5 mg/ml),dissolved in 0.5 M borate buffer (pH 10.0), 1-100 mg of activated PEG₂is added. The mixture is stirred at 37° C. for 1 h to complete thereaction: amino groups in lysine residues and N-terminal amino groupsare modified with activated PEG₂ to form PEG-protein.

In another embodiment, PEGylation is carried out as follows (J. J. Kimand K. Park, Pharmaceutical Research 18, 794 (2001)). 100 mg of proteinis dissolved in 10 ml of 0.1 M borate buffer, pH 8.5, and the solutionis kept in an ice bath. Monomethoxy poly(ethylene glycol) p-nitrophenylcarbonate (MPEG-NPC) is slowly added to the protein solution at varyingconcentrations to modify the degree of PEGylation. The temperature isthen gradually increased from 4° C. to room temperature, and thesolution allowed to react for 20 hours. The resulting solution isdialyzed exhaustively against deionized water and lyophilized to obtainpurified PEG-protein.

To encapsulate the therapeutic agent in a cross-linked polymer, asolution of an appropriate cross-linking agent may be added to asolution of the desired biodegradable polymer and therapeutic agentunder conditions to allow the cross-linking agent to interact with thepolymer. The interaction cross-links the polymer, encapsulating thetherapeutic agent. In an alternative embodiment, the therapeutic agentis covalently or non-covalently linked to the biodegradable polymer. Thebiodegradable polymer and the cross-linking agent may include one or theother of an indicator analog and its corresponding cross-link receptor.

One skilled in the art can easily optimize the cross-linking conditionsthrough routine experimentation. For example, an excess of divalent ionssuch as calcium and magnesium promote the cross-linking of dextran byplant lectins. Calcium alone is typically sufficient to promotecross-linking with mammalian lectins, but higher concentrations aregenerally needed. The optimal concentration of divalent ion may bedetermined by producing gels with various concentrations of calciumand/or magnesium. Likewise, the cross-linking efficiency and indicatorsensitivity of the gel may be optimized by using the techniquesdescribed in Example 1.

For example, the optimal concentration of PHA or an artificialmultimeric glucose binding protein may be determined by adding aconcentrated solution of PHA containing 1 mM to 100 mM of calcium toeach of several solutions containing varying concentrations of dextranor other biocompatible polymer. Alternatively, insulin-polysaccharideconjugates or insulin-polymer conjugates containing glucose or mannoseresidues may be combined with the cross-linking agent. The cross-linkingefficiency and glucose sensitivity of the gels may then be determined asdescribed in Example 1. The insulin release may be monitored asdescribed in Example 3. One skilled in the art will recognize that thesame techniques may be used to determine the cross-linking efficiency,indicator sensitivity, and therapeutic agent release of other gelsproduced using the techniques of the invention.

In one embodiment, the cross-linked polymer is an insoluble hydrogel.The hydrogel only degrades as competition from the indicator with theinteraction between the cross-linking agent and the indicator analoginterrupts the cross-links. The hydrogel degrades in a layer-by-layerfashion from the outside in, allowing the therapeutic agent to bereleased at an approximately constant rate as the hydrogel degrades. Thehydrogel may be implanted at a site in a patient, where it will deliverthe therapeutic agent at a relatively constant rate with respect to thelocal level of the indicator.

Such a material is optimal for one-time therapies, for example, aftersurgery. The hydrogel degrades completely as the therapeutic agent isdelivered, obviating a second surgical procedure to remove the drugdelivery device. Alternatively, the material may be injected into apatient. Even where a patient requires long term treatment, thedegradation mechanism of the drug delivery material can reduce thefrequency of injections by preventing the therapeutic agent from beingwasted. The agent is only released as needed, not constantly.

Alternatively, the cross-linked polymer may be fabricated as a mass ofnanoparticles through a reverse microemulsion (RM). RMs arespontaneously forming, thermodynamically stable, dispersed systemshaving a uniform particle size in the range of 2-200 nm (FIG. 2). Ingeneral, an aqueous core 2 is stabilized by a non-ionic surfactant 4 ina continuous oil phase 6. These structural characteristics make RM's anideal medium for the controlled synthesis of ultrafine particles.Because the resulting nanoparticles will be used for drug deliveryapplications, it is highly desirable to construct these systems withbiocompatible surfactants and oils. Such systems constructed fromsoybean and sunflower seed oils, as well as food-grade surfactants suchas sorbitan esters and ethoxylated fatty esters, have been characterizedby several researchers (P. P. Constantinides, et al., Pharm. Res. 11,1385 (1994)). Appropriate oils include soybean oil, (Sigma-Aldrich),Arlacel 186, (a mixture of mono and diglycerides of fat-forming fattyacids available from ICI Surfactants), Captex 355 (a mixture oftriglycerides of caprylic and capric acids available from AbitecCorporation), Capmul MCM, (a mixture of mono-diglycerides of mediumchain caprylic and capric fatty acids available from AbitecCorporation), Myvacet (a mixture of acetylated monoglycerides availablefrom Eastman Chemical Company), and Myverol 18-92 (a monoglycerideproduced from canola oil available from Eastman Chemical Company).Combinations of these oils may be used to optimize the composition ofthe RM. Exemplary surfactants include Tween 80 (polyoxyethylene20-sorbitan monooleate, available from ICI Surfactants), Span 80(sorbitan monooleate, available from ICI Surfactants), and Cremophor EL(ethoxylated high purity castor oil available from BASF Corporation).The RM should be optimized to prevent the development of large droplets,e.g., larger than about 500 nm.

The procedure for synthesizing RMs depends in part on the stability ofRMs in the presence of the encapsulated materials. In general, thepolymer, cross-linking agent, and therapeutic agent are combined in theaqueous phase under conditions that minimize cross-linking. The aqueousphase is then combined with a mixture of surfactant and oil. Theemulsion is treated to favor the interaction between the polymer chainsand the cross-linking agent, causing the polymer chains to cross-linkwithin and around the aqueous domains. For example, the pH may beadjusted or the temperature changed. Some time may be allowed for theparticles to form, after which the particles are separated from themedia, for example, by centrifugation, and washed in a hydrogen-bondingsolvent such as ethanol. The separation and rinsing steps may berepeated several times to ensure complete removal of oil and surfactant.The particles are then washed with aqueous buffer to removeuncross-linked polymer chains and loosely encapsulated therapeutic agentand dried. One skilled in the art will recognize that composition,temperature, and the choice of RM system may all be optimized to achievea desired particle size and morphology.

Particles formed in RMs may be used to deliver the therapeutic agentthrough injection, ingestion, or inhalation. As a result, thesematerials are useful for repeated administration of the therapeuticagent. For example, oral or ingestable insulin would reduce the numberof injections required by diabetics and provide insulin in quantitiesmore closely related to the metabolic cycle of the patient. Thenanoparticle 8 degrades to release the therapeutic agent 10, and the nowuncross-linked polymer chains 12 are degraded hydrolytically orenzymatically (FIG. 3). Particle size may be optimized depending on thedelivery vehicle, desired residence time, and other factors. In someapplications, particles having a size of about 100 m to 300 nm or 300 nmto 500 nm may be employed.

Alternatively, coarse emulsions may be used to produce larger particles.Smaller amounts of surfactant are employed and the solutions are mixedto promote the formation of droplets. FIGS. 15A, 18, and 19 all depictcompositions where larger particles are formed, as evidenced by thecloudiness of the mixture of oil, water, and surfactant. In someembodiments, particles may have a size of, for example, 500 nm to 5 μm,5 μm to 50 μm, 50 μm to 100 μm, or even larger.

Stimuli-responsive particles may be synthesized in aqueous solutionthrough self assembly. In one embodiment, the therapeutic agent isattached to the biocompatible polymer. Because the biocompatiblepolymer-therapeutic agent complex associates through affinity bindingwith the cross-linking agent, there is less need for reactioncompartmentalization as described in the RM synthesis. In general, asolution containing the cross-linking agent is combined with a secondsolution containing the biocompatible polymer-therapeutic agent underconditions to promote cross-linking. In one example, a Con A solution at10 mg/ml in a 20 mM pH 7.0 BES buffer containing 1 mM Ca²⁺, 1 mM Mn²⁺,and 1 M NaCl was combined with a dextran-insulin solution at 1 mg/ml ina 20 mM pH 7.0 BES buffer containing 150 mM NaCl. Precipitated particlesformed within minutes that were centrifuged, washed repeatedly, andfreeze-dried to obtain a powder. The powder was dissolved in bufferedsaline solutions containing glucose at concentrations varying between 50and 500 mg/dl. The resulting insulin-dextran dissolution from theparticles increased with increasing glucose concentration in a mannersimilar to the gels and RM-derived nanoparticles. This procedure iseasily performed aseptically and does not require large amounts of oiland surfactants to carry out.

Fluorophores such as fluorescein isothiocyanate (FITC),tetramethylrhodamine isothiocyanate (TRITC), and rhodamineisothiocyanate (RITC) may be used with the drug delivery vehicles of theinvention. One skilled in the ar will recognize that other biocompatiblefluorophores may also be employed. For example, a fluorophore may belinked to the biodegradable polymer or cross-linking agent orencapsulated in the cross-linked polymer. For a cross-linked polymerdelivered subcutaneously, fluorescence spectroscopy using standardclinical autofluorescence techniques may be used to determine the amountof cross-linked polymer still present and whether the patient needs anew dose. In general, a light source and a detector are disposed on apatient, for example, on a finger or arm. The light source excitesluminescence of a particular species in the body, which is thendetected. Autofluorescence techniques may also be used to determine theamount of the therapeutic agent that has been released in the blood. Thefluorophore and the therapeutic agent are released together, and theamount of one can be correlated to serum levels of the other.Alternatively, the fluorophore may be cleared by the kidneys, andfluorescent measurements of urine may be used to determine either howmuch therapeutic agent has been released or simply whether thecross-linked polymers have completely degraded.

In one embodiment, self-quenching fluorophores are used in thecross-linked polymer. Both the biocompatible polymer and thecross-linking agent are labeled with fluorophores. The photon emitted byone fluorophore is absorbed by the other, with non-luminescentrelaxation. As the cross-linked polymer degrades, the biocompatiblepolymer and the cross-linking agent are separated, allowing the photonto be detected externally instead of quenched.

Fluorophores may also be used to facilitate pharmacokinetic studies. Therate with which a therapeutic agent is transported from a subcutaneousor intramuscular site to another site in the body may be measured bymeasuring the fluorescence of an agent released from the cross-linkedpolymer along with the therapeutic agent. Alternatively, the fluorophoremay be used to determine the rate of in vivo degradation and how thatrate changes as the volume of the cross-linked polymer changes. Afluorophore linked to the therapeutic agent can also help determine therate of non-stimuli responsive leakage from the cross-linked polymer.

EXAMPLE 1 Glucose-Sensitive Hydrogels for Delivery of Insulin

Material Selection

Con A, a lectin derived from the jack bean plant, was initially chosenas the glucose-binding protein because it is inexpensive, readilyavailable, and extensive work has already been done to evaluate itssugar binding properties. Con A-derived systems represent a tractablemodel for development of insulin-delivery vehicles employing alternativesugar-binding proteins such as human mannan binding lectin (MBL).

Because the end application requires repeated dosage, the biodegradablepolymer is preferably biocompatible and biodegradable to avoidpotentially harmful accumulation. Dextran, poly(α-D-glucose), isattractive because it binds Con A, is available at molecular weightsranging from 2K to 2000K, and is already FDA approved for use as a bloodplasma volume expander. Dextran is also a versatile molecule, capable ofbeing covalently modified at the free —OH groups with a variety ofchemicals, drugs, and proteins (R. Mehvar, J. Control. Release 69, 1(2000)). For example, conjugation with fluorescein isothiocyanate(FITC-Dex) permits independent analysis of the efficiency of particlecross-linking and glucose sensitive dissolution. As detailed below, weexploited three exemplary modifications: (1) fluorescent labeling, (2)glycosylation, and (3) drug conjugation.

Gel Synthesis and Characterization

Previous attempts at forming glucose-sensitive gels from dextrans andother polysaccharides have resulted in extraordinarily slow responses tophysiological glucose concentrations, an inability to tune the glucoseresponse, and non-specific insulin leakage from the gels. (J. J. Kim, K.Park, J. Control. Release 77, 39 (2001); S. Tanna, et al., J. Pharm.Pharmacol. 11, 1461 (2002)) In addition, due to the more viscous thanplastic nature of the gels, they could not be readily isolated tomeasure their insulin release properties. We have discovered a set ofmaterial parameters and synthesis conditions that result in gels of ConA and dextran with superior glucose response and mechanical stabilitythan those previously synthesized.

For each experiment, 0.100 ml of Con A, dissolved at 100 mg/ml in 20 mMBES buffered saline containing 1 mM Mn²⁺, 1 mM Ca²⁺, and 1 M NaCl, wasadded to 0.100 ml of a dextran solution, dissolved at a knownconcentration in 20 mM BES buffered saline containing 150 mM NaCl. Thesolutions were allowed to react for one hour, after which the resultinggels were separated from the supernatant. The gels were washed twicewith 1 ml of BES buffered saline solution and freeze-dried. To evaluatethe amount of dextran participating in the gel reaction as a function ofdextran molecular weight (MW) and Con A/dextran ratio, the dextrans werefluorescently labeled to easily detect their concentration in solution(MW 70 K and 170 K labeled with tetramethylrhodamine isothiocyanate(TRITC), MW 280 K and 500 K labeled with fluorescein isothiocyanate(FITC)). The fluorescence of in each of the supernatants was measuredusing a Molecular Devices fmax fluorescence spectrophotometer (TRITC:λ_(ex)=544 mm, λ_(em)=590 nm; FITC: λ_(ex)=485 mm, λ_(em)=538 nm), andconverted to concentrations using a set of standard curves.

$\begin{matrix}{X_{CL} = \frac{\lbrack{dextran}\rbrack_{total} - \lbrack{dextran}\rbrack_{supernatant}}{\lbrack{dextran}\rbrack_{total}}} & (1)\end{matrix}$

Crosslinking efficiency (X_(CL)) was calculated according to Equation 1and found to vary with both the Con A/dextran ratio and the dextran MW(FIG. 4). For each MW, X_(CL) reaches a maximum at a Con A/dextran ratioof about six. Soluble Con A-dextran complexes rather than insolublenetworks form at lower ratios due to an insufficient number of proteinbinding sites. At higher ratios, precipitates form that are virtuallyinsensitive to sugar concentration. The maximum X_(CL) is only 60% forthe dextran with MW=70 K, but increases to 90% for the higher MWdextrans. It appears that lower MW dextrans can form soluble ConA-polymer conjugates that do not gel, thereby decreasing the X_(CL).

Glucose-Sensitive Gel Dissolution

Freeze-dried gels synthesized at a Con A/dextran ratio of 6.1 fromdextran of MW=70 K (Dex-70) and dextran of MW=500 K (Dex-500) wereplaced in 20 mM pH 7 buffered saline solutions containing 50, 100, and400 mg/dl glucose. Gel dissolution was measured by detecting dextranfluorescence in the supernatant and normalizing the calculatedconcentrations to those obtained after complete dissolution. The gelsdissolve at markedly different rates depending on the glucoseconcentration in the release medium. The Dex-70 (FIG. 5) and Dex-500(FIG. 6) exhibit sustained degradation over days at low glucoseconcentrations, but completely dissolve in about two hours at 400 mg/dl.The Dex-70 gels dissolve faster at the lower glucose concentrations thanthe Dex-500 gels and are more sensitive to changes between 50 and 100mg/dl.

Freeze-dried Dex-500 gels were also dissolved in buffered salinesolutions at 37° C. to determine the effect of temperature ondissolution rates. As shown in FIG. 7, the Dex-500 gels are moreglucose-sensitive and dissolve faster at elevated temperatures. In fact,at 37° C., the gels clearly distinguish between 50 mg/dl (hypoglycemic),100 mg/dl (normal), and 400 mg/dl (hyperglycemic) glucoseconcentrations, representing an ideal formulation for practicalapplication. The temperature-dependent effects may be due to an increasein Con A binding affinity for free glucose versus polymeric glucose,leading to gel disruption at lower free sugar concentrations. Anotherpossible explanation is a temperature-dependent increase in polymerdiffusion from the gel after competitive binding has taken place.

FIGS. 5-7 demonstrate glucose-sensitive gel dissolution, but fail toquantify two key points: (1) intrinsic glucose-sensitivity (IGS), therange of glucose concentrations over which there is significantdissolution, and (2) reversibility of response. To determine the IGS foreach of the materials, we constructed a flow cell as shown in FIG. 8.The inlet to the flow cell is connected to two reservoirs containingbuffered saline solutions with low and high glucose concentrations. Thegels were equilibrated at 0 mg/dl for two hours and then the inletglucose concentration was ramped at a rate of 8.3 mg/dl/min by changingthe ratio of flow rates from the two reservoirs. The outlet of the flowcell was connected to an absorbance detector to continuously determinethe amount of dextran dissolved at a wavelength equal to the maximumλ_(ex) of the dextran fluorophore.

The amount of dissolved dextran was integrated over time and normalizedby that originally contained within the gel (FIG. 9). In addition,samples were taken at regular intervals and diluted appropriately tomeasure the glucose concentration with a Prestige™ Smart System glucosemeter. The glucose concentration was confirmed to vary linearly overtime at the predetermined rate of 8.3 mg/dl/min. In this experiment, 10%of the Dex-70 gel dissolved before the glucose concentration reached 600mg/dl and 90% by 860 mg/dl. Current experiments are aimed at correlatingglucose concentration at 10% gel dissolution (G_(10%)) for gels thatdemonstrate markedly different release profiles in the batch experimentsoutlined before. The goal was to obtain a single parameter, such asG_(10%), that captures the IGS for each formulation.

To determine the reversibility of response, the flow cell experiment wasadapted to cycle the inlet glucose concentration from a low to highvalue in 30 min and then back down again in another 30 min. Geldissolution was monitored by continuously measuring the absorbance atλ_(max) (544 nm) of the fluorescently labeled dextran. FIG. 10 showsthat the gels are capable of releasing at a higher rate as the glucoseconcentration increases, but, more importantly, can also slow down theirrelease as the glucose concentration decreases. As expected, the extentof the response is governed by the overall glucose concentration range.When the gels are cycled between 50 and 500 mg/dl, the extent of theresponse diminishes more rapidly after each cycle as the gel approachescomplete dissolution. The flow cell, therefore, represents a powerfultool for characterizing both the glucose sensitivity and dynamicresponse of our materials.

EXAMPLE 2 Modifying Glucose Sensitivity of Hydrogels

Although the Con A-dextran gels appear to respond remarkably well toglucose concentrations in the physiological range, it may be beneficialto modify the gel IGS for certain practical situations. Depending on thesite of application (e.g. subcutaneous tissue, intravenous circulation,specific organs, etc.), the local sugar concentration may vary a greatdeal for a given physiological state, such as fasting or post-prandial.For example, changes in glucose concentration in the subcutaneous fluid(SCF) are well correlated to changes in intravenous (IV) concentration,but the average value in the SCF may be much lower (S. J. Updike, M. C.Shults, B. J. Gilligan, R. K. Rhodes, Diabetes Care 23, 208 (2000)). Inaddition, one may desire more than one type of glucose-regulatedresponse. One material may be designed with an IGS for normoglycemicconcentrations to provide well-regulated long-term insulin release.Another material may be designed with a much higher IGS to releaseinsulin only after meal-time blood sugar rises. Because the dextran-ConA materials exhibit significant degradation at normoglycemicconcentrations, we developed methods to increase the IGS throughcovalent glycosylation of the dextran polymer.

Mannose is known to bind Con A with 3.8 times the affinity as glucose(J. N. Sanders, S. A. Chenoweth, F. P. Schwarz, J. Inorg. Biochem. 70,71 (1998)). Therefore, it is expected that covalent modification ofdextran with mannose will result in a gel that only responds to muchhigher sugar concentrations. Dextran was modified with mannose toproduce mannosylated dextran (ManDex) using the divinylsulfone (DVS)procedure described in R. Ballerstadt, J. S. Schultz, Anal. Chim. Acta345, 203 (1997), the contents of which are incorporated herein byreference. Briefly, FITC-Dex is added to a pH 11.4 bicarbonate bufferand activated with DVS. D-mannose is then added and allowed to react for˜1 hour at room temperature, after which glycine is added to neutralizeand quench the reaction. The resulting polymer is dialyzed exhaustivelyagainst deionized water and finally lyophilized.

Gels constructed from ManDex-70 at a Con A/ManDex ratio of 6:1 wereplaced in the flow cell and the inlet glucose concentration was cycledbetween 50 and 250 mg/dl (a) and 50 and 500 mg/dl (b), as was done forthe unmodified Dex-70 gels. FIG. 11A shows that the gel response is evenmore reversible than the unmodified case, especially for the 50-500mg/dl cycle. A majority of the gel was still intact after the sixcycles, indicating increased IGS for the ManDex formulation. FIGS. 11Band 11C show that mannosylation significantly slows dissolution.

EXAMPLE 3 Insulin Encapsulation and Release

The dextran gels were originally designed to have a pore structure thatinhibits insulin diffusion at low sugar concentrations, but releasesinsulin as the gel dissolves at higher concentrations. To load the gelswith insulin, the synthesis media was modified to contain a solution ofbovine insulin at 1 mg/ml. After synthesis and washing, the Dex-70 gels(Con A/dextran=6.1 (w/w)) contained approximately 1% bovine insulin on adry weight basis as determined by HPLC using a C18 column (WatersSymmetry 5 mm C18, 250×4.6 mm) and a mobile phase of 1.4 ml/mincontaining 37% v/v acetonitrile in a pH 2.4 sodium sulphate/phosphoricacid buffer. The insulin-loaded gels were then placed in pH 7 bufferedsaline containing glucose concentrations of 50, 100, and 400 mg/dl, andsamples were taken at regular time intervals to measure both dextran andinsulin release by HPLC.

FIG. 12A shows that insulin release profiles are indistinguishablebetween 50 and 100 mg/dl, but much more rapid at the higher 400 mg/dlglucose concentration. At the low sugar concentrations, gel dissolutionis fairly slow, as shown in FIG. 12B, but the pore size and porosity arequite high, as shown in the ESEM micrographs (FIG. 13). Insulin releaseis therefore governed by hindered diffusion through the porous gel atlow sugar concentrations. At 400 mg/dl, the gel completely dissolves,thereby releasing the entire insulin content.

We have employed two methods to improve control over insulin releaserates at low sugar concentrations. One way is to modify the gel poresize to approach that of the insulin molecule and then increase the poresize considerably in response to small increases in glucoseconcentration. To accomplish this, the dextran was modified withpolymerizable methacrylate groups according to the procedure describedpreviously to provide sites for chemical crosslinking (S. H. Kim, C. C.Chu, J. Biomed. Mater. Res. 49, 517 (1999)). The chemically crosslinkedgels indeed allow minimal insulin release at low sugar concentrations,but fail to respond at elevated sugar concentrations (FIG. 12C). Inthese cases, the glucose-insensitive chemical crosslinking dominates thepore structure and the resulting insulin release profiles.

The second method, which has shown considerable promise, is to closelyassociate insulin to the dissolving dextran. By doing so, the insulinrelease would exactly match the gel dissolution profiles. Significantresearch has been carried out over the years to graft proteins anddrugs, including insulin, to dextran in an effort to modify theircirculation time and absorption profiles. The most common conjugationmethod involves activating dextran with cyanogen bromide (CNBr) at pH 10in water, followed by reaction with insulin (L. Kagedal, S. Akerstrom,Acta. Chem. Scand. 25, 1855 (1971)). Using this method, insulin has beenconjugated to dextran of MW's between 10 and 2,000 kDa with degrees ofsubstitution (DS) ranging between 1% and 30%. The reported bioactivityof the conjugates varies between 10% and 100% of unmodified insulin, butin all cases a glucose lowering effect was observed in vivo (L. Kagedal,et all, Acta. Chem. Scand. 25, 1855 (1971); K. J. Armstrong, M. W.Noall, J. E. Stouffer, Biochem. Biophys. Res. Commun. 47, 354 (1972); Y.Sakamoto, Y. Akanuma, K. Kosaka, B. Jeanrenaud, Biochim. Biophys. Acta498, 102 (1977); F. Suzuki, Y. Daikuhara, N. Ono, Y. Takeda,Endocrinology 90, 1220 (1972)).

The degree of insulin substitution was determined by UV spectroscopy at280 nm and confirmed by the Bradford protein assay to be 36±4% (w/w).Gels were formed from Con A and dextran-insulin according to theprocedure described before. The insulin encapsulation efficiency wasfound to increase by over an order of magnitude and the insulin loadingincreased by almost 8× through insulin conjugation. ConA-dextran-insulin gels with a Con A/dextran-insulin ratio of 4 wereplaced in pH 7 buffered saline solutions containing 50, 100, and 400mg/dl of glucose, and samples were taken at regular time intervals tomeasure the dextran-insulin release. The dextran-insulin concentrationwas determined by HPLC using a SuperDex G75 column (AmershamBiosciences) and a pH 7 BES buffered saline mobile phase of 1.0 mmin.The Superdex column separates any Con A released, so that thedextran-insulin may be uniquely determined at λ=280 nm.

The dextran-insulin release profiles of Dex-70 gels with ConA/dextran-insulin=4 (w/w) shown in FIG. 14 demonstrate remarkably lowinsulin leakage at the lower sugar concentrations and rapid release atthe hyperglycemic glucose concentration of 400 mg/dl.

EXAMPLE 4 In Vivo Evaluation

Con A was dissolved in pH 7 BES buffer containing 1 M NaCl and 1 mM Mn²⁺and Ca²⁺ at a concentration of 100 mg/ml and sterile filtered through a0.45 micron syringe-driven membrane filter. Dextran (70 K)functionalized with 15% human insulin (w/w) was dissolved in pH 7 BESbuffer containing 0.15 M NaCl at a concentration of 20 mg/ml and sterilefiltered through a 0.45 micron syringe-driven membrane filter. Gels weresynthesized in a sterile laminar flow hood using standard asepticprocedures by combining 0.20 ml of Con A solution with 0.20 ml ofdextran-insulin solution (single dose), 0.40 ml of Con A solution with0.40 ml of dextran-insulin solution (double dose), or 0.60 ml of Con Asolution with 0.60 ml of dextran-insulin solution (triple dose). Theresulting gels were isolated and washed exhaustively with sterilephosphate buffered saline solution and stored overnight prior totransplantation.

Male Sprague-Dawley rats (Charles River Laboratories) weighingapproximately 250 g were injected with 80 mg/kg of streptozotocin toinduce diabetes. After one week, rats with blood glucose levels greaterthan 300 mg/dl were used in the following experiments. Gels (experiment)or saline (control) solution were placed in the intraperitoneal cavitythrough an incision in the abdominal skin and muscular layers. Bloodsamples were taken from the tail vein over time and measured for glucoseconcentration using a MediSense glucometer. FIG. 32 demonstrates theability of a single dose to control diabetic glucose levels over a oneand a half day period. Furthermore, FIG. 33 shows that glucose controlis extended to three days by just tripling the dose of glucose-sensitivegel.

In another experiment double dose gels (experiment) or saline (control)solution were placed in the intraperitoneal cavity through an incisionin the abdominal skin and muscular layers. The rats were fasted in themorning for six hours, and blood samples were taken from the tail veinafter fasting and measured for glucose concentration using a MediSenseglucometer. FIG. 34 demonstrates the ability of a double dose gel tocontrol diabetic fasting glucose levels over a two and a half dayperiod. In select animals, an intraperitoneal glucose tolerance test(IPGTT) was performed after the six hour fast. The IPGTT was performedby injecting a 45% glucose solution intraperitoneally at a dose of 1g/kg of body weight. Blood samples were taken at frequent intervals overthe course of two hours. FIG. 35 shows the ability of double dose gelsto minimize the extent and timing of the spike in blood glucose levels.The glucose tolerance compares favorably to that obtained fromnormal-non diabetic rats subjected to the same procedure.

EXAMPLE 5 Reverse Microemulsion Formulation

The existence of RM's was identified by preparing various pseudoternarycompositions and evaluating the optical clarity of the mixture. Clear,transparent formulations are indicative of stable RM's as the size ofthe aqueous domains are much smaller than the wavelength of light (M. J.Lawrence, G. D. Rees, Adv. Drug Deliv. Rev. 45, 89 (2000)). To quantifythe optical clarity of a particular system at a number of compositionswhile minimizing the experimental time and materials required, a rapidscreening approach was developed. Briefly, varying amounts of surfactant(3:2 w/w Tween 80/Span 80) and oil (3:1 w/w Captex 355/Capmul MCM) weremicropipetted into a glass, flat-bottomed, 96-well microplate (500 μlwell capacity, Alltech) and mixed thoroughly. The appropriate amount ofaqueous solution was then added to make a total volume of 350 μl, andmixed in such a way that each well contained a specific ternarycomposition. Each composition was run in duplicate, and absorbancevalues for all 96 wells were collected at a wavelength of 450 nm using aVERSAmax microplate reader (Molecular Devices, Sunnyvale, Calif.) toquantify turbidity.

The data resulting from such experiments were plotted on a pseudoternarycontour diagram, thereby yielding a pseudoternary surface. FIG. 15Adepicts the pseudoternary surface obtained from our rapid screeningapproach, which agrees remarkably well with the one in the literatureobtained by multiple cloud point titrations (S. Watnasirichaikul, N. M.Davies, T. Rades, I. G. Tucker, Pharm. Res. 17, 684 (2000)). DLS results(FIGS. 15B-D) obtained at select ternary compositions confirm reversemicroemulsion (RM) existence throughout the region of opticaltransparency. As the aqueous concentration, φ_(A), increases at aconstant concentration of surfactant, φ_(S), (FIG. 15B) and at aconstant concentration of oil, φ_(O) (FIG. 15C), the dispersed phaseprogresses from reverse micelles to larger water-swollen reversemicelles until finally a turbid multi-phase region is obtained. As φ_(S)increases at a constant φ_(A) (FIG. 15D), the system transitions from akinetically stabilized reverse emulsion toward a RM containing dropletsof decreasing diameter.

Temperature also influence the formation of RMs containing Con A orinsulin. As the temperature increases, less surfactant is required tomaintain the desired dispersed phase (FIG. 16). In addition, FIG. 16demonstrates that, generally, RMs formed at room temperature will notcoalesce at higher temperatures, for example, after administration to apatient. The increase in the region of optical clarity also indicatesthat an increase in temperature during fabrication can increase theyield of particles from a given microemulsion.

EXAMPLE 6 RM Stability in the Presence of Con A, Insulin, or Dextran

Our early research found that the addition of either Con A or insulintransformed an otherwise optically transparent and stable RM into aturbid, coarse emulsion. FIG. 17 shows the resulting increase in dropletsizes as a function of concentration of both Con A and insulin whendissolved in a pH 7 buffered saline aqueous phase using an RMcomposition of φ_(A)=0.10, φ_(S)=0.25, φ_(O)=0.65. However, when theproteins were dissolved in a 0.1 N HCl solution, the resulting RM wasoptically transparent and the size of the dispersed domains approachedthat of the control.

Possible explanations include pH-dependent differences in proteincharge, state of aggregation, and tertiary structure. For example, bothCon A and insulin form tetramers and hexamers respectively at neutralpH, which may result in decreased solubility in the RM aqueous domainsand increased droplet aggregation. In addition, other researchers haveobserved large structural changes when proteins were added to reversemicelles as was the case, for instance, with cytochrome c, whichenhanced percolation due to increase of attractive interactions betweenreverse micelles (C. A. T. Laia, W. Brown, M. Almgren, S. M. B. Costa,Langmuir 16, 465 (2000)). In our system, these attractive interactionsare minimized at low pH, but increase upon neutralization.

To evaluate the effect of dissolved proteins and polymers on RM phasebehavior, varying concentrations of each component were dissolved in a0.1 N HCl aqueous phase before addition to the surfactant/oil mixture.Insulin has minimal effect on the RM existence region as compared to thecontrol (FIG. 18), while Con A gives rise to two distinct regions ofoptical clarity separated by a turbid region at high surfactant,moderate oil concentrations (FIG. 19).

To determine the extent to which the RM formulation contributes to theprotein-induced instability at neutral pH, two other biocompatible RMsystems were investigated. One system, Myvacet, is constructed from aMyvacet/Capmul MCM/Myverol 18-92 oil and Cremophor EL surfactant phase.The other system, Soybean, is constructed from a Soybean Oil/Arlacel 186oil and Tween 80 surfactant phase. FIG. 20 illustrates the droplet sizefor each system as a function of protein concentration using a pH 7 BESbuffered saline aqueous phase and φ_(A)=0.03, φ_(S)=0.10, andφ_(O)=0.87. The results indicate that the Soybean system is minimallyaffected by the presence of insulin and Con A, while the droplet sizesfor the Myvacet system are between those of the Captex and Soybeansystems.

FIG. 21 illustrates the effect of dissolved dextran on RM formation. RMswere formed by dissolving dextran in a 0.1 N HCl aqueous phase andadding it to a mixture of surfactant (3:20 w/w Tween 80/Span 80) and oil(3:1 w/w Captex 355/Capmul MCM) at 25° C. For dextran having MW=10,lower concentrations of dextran result in a uniform region of opticalclarity, while increasing concentrations result in development of aturbid region at high surfactant concentrations (FIG. 21A) increasingthe molecular weight magnifies this effect. FIG. 21B illustrates thatthe relationship between RM diameter and [dextran] varies with molecularweight but indicates that, regardless of concentration, a molecularweight of 10 results in RMs having a diameter of at least 100 nm.

EXAMPLE 7 Nanoparticle Synthesis, Recovery, and Characterization

Glucose-sensitive nanoparticles were prepared using a RM formulationcomprising 65% v/v oil (3:1 w/w Captex 355/Capmul MCM), 25% v/vsurfactant (3:2 w/w Tween 80/Span 80), and 10% v/v aqueous phase. To 1.8ml of a premixed solution of oil and surfactant, 160 μl of a 0.1 N HClsolution containing Con A and dextran of predetermined concentrationswere added and mixed thoroughly. Next, 20 μl of a pH 7.0 200 mM BESbuffered saline solution containing 1 M NaCl and 20 mM MnCl₂ and CaCl₂and 20 μl of a 1 N NaOH solution were added in succession to neutralizethe pH and activate Con A/dextran crosslinking. The particle-containingRMs were diluted 1:10 (v/v) with ethanol and centrifuged for 30 min toseparate the particles from the ethanol, oil and surfactant. Thecentrifuge cake was redispersed by sonication and washed twice inethanol to remove residual oil and surfactants, followed by washing with20 mM pH 7.0 BES buffered saline solution to remove any unbound dextran.The remaining material was redispersed in ethanol by sonication anddried under vacuum at room temperature for environmental scanningelectron microscopy (ESEM) studies (FEI/Philips XL30 FEG ESEM).

FIG. 22 is an ESEM micrograph of nanoparticles obtained from aformulation comprising Dex-280 at 8 mg/ml and Con A at 50 mg/ml andφ_(A)=0.10, φ_(S)=0.25, and φ_(O)=0.65. In this RM system, the particlesobtained are much larger than the original aqueous domains, mostprobably due to the pH-dependent change in RM phase behavior. Inaddition, one would expect that the interaction between Con A anddextran increases droplet attraction, leading to particle growth. Theentire population of particles is present in the submicron range,demonstrating our ability to restrict the reaction size domain and formphysically crosslinked nanoparticles via RM-mediated synthesis.

To evaluate the amount of dextran participating in the nanoparticlecrosslinking reaction as a function of dextran molecular weight and ConA/dextran ratio, the dextrans were fluorescently labeled (FITC) asbefore to easily detect their concentration in solution. FIG. 23illustrates the amount of crosslinked dextran versus the amount loadedinto the RM for [Con A]_(aq)=50 mg/ml. As before, both Dex-40 andDex-280 demonstrate a strong dependence of the amount of crosslinking on[Con A] (FIG. 24). The results show that as [dextran] decreases at aconstant [Con A], the extent of crosslinking increases and reaches amaximum at [Con A]/[dextran] between 3 and 6. The amount of crosslinkedpolymer is improved by a factor of 5 by increasing the dextran MW to 280K. Mannosylation of dextran of both MW's also results in a greaterextent of crosslinking over a range of [Con A]/[dextran] ratios (FIGS.23-24). The higher affinity of Con A for mannose(K_(d,glucose)=3.8K_(d,mannose)) ensures a higher proportion of boundpolymer at a given concentration of Con A and dextran (J. N. Sanders, etal., J. Inorg. Biochem. 70, 71 (1998). In addition, mannosylation of thedextran backbone effectively increases the degree of branching, which isknown to facilitate the precipitation reaction between Con A andα-1,6-linked polysaccharides (I. J. Goldstein, C. E. Hollerman, J. M.Merrick, Biochim. Biophys. Acta 97, 68 (1965)).

EXAMPLE 8 Glucose Sensitive Degradation of Nanoparticles

To obtain the IGS for nanoparticles of different composition, theisolated nanoparticles were redispersed in a known volume of pH 7.0 BESbuffer containing 0.150 M NaCl and 1 mM Mn²⁺ and Ca²⁺ ions. Thedispersion was mixed for 30 min at room temperature, followed bycentrifugation for 30 min to separate the particles from the aqueousmedium. Half the volume was collected for analysis and replaced with ahigher concentration glucose buffer. The collected samples were analyzedusing an fmax fluorescence spectrophotometer with λ_(ex)=485 nm andλ_(em)=538 nm to determine the amount of dextran dissolved from thenanoparticles after each step.

Plotting the percent of nanoparticle dissolution as a function ofglucose concentration for the Dex-280 (FIG. 25) shows that glucosesensitivity may be controlled based on the relative ratio of Con A topolymer. Increasing the Con A/dextran from 1.6 to 6.3 (w/w) results inparticles that are more sensitive to higher glucose concentrations. Inaddition, ManDex-280 nanoparticles have almost an order of magnitudehigher IGS than unmodified nanoparticles. The combination of ConA/dextran ratio and degree of mannosylation provides a convenient meansfor fine tuning the nanoparticle glucose-sensitivity for anyapplication. FIG. 26 shows that the degree of cross-linking stronglyinfluences glucose sensitivity. Both insufficient and excess cross-linkdensity greatly decrease the sensitivity of particle dissolution toglucose concentration. There is an optimal ratio of dextran 20 to Con A22 where their interaction transitions from a dextran-limited regime toa Con A limited regime (FIG. 27). At this ratio, the dextran iscross-linked the most effectively, resulting in the highest dextranrelease upon increasing the glucose concentration.

Nanoparticles synthesized at a Con A/dextran ratio of 3.1 from Dex-280(FIG. 28) and a Con A/dextran ratio of 6.1 from ManDex-280 (FIG. 29)were placed in 20 mM pH 7 buffered saline solutions containing 0, 100,and 1000 mg/dl glucose. Dissolution was measured by detecting dextranfluorescence in the supernatant and normalizing the calculatedconcentrations to those obtained after complete dissolution. As with thegels, the nanoparticles dissolve at markedly different rates dependingon the glucose concentration in the release medium. Most importantly,the mannosylated nanoparticles demonstrate sustained dissolution over anentire day even at the extremely high glucose concentration of 1,000mg/dl, while the unmodified nanoparticles completely dissolve in lessthan an hour at the same glucose concentration.

EXAMPLE 9 Release Profiles of Insulin-Containing Nanoparticles

Zn²⁺-free bovine insulin (Sigma-Aldrich) was dissolved in the aqueousphase of select compositions, and the amount released was determined byhigh-performance liquid chromatography (HPLC) using 37% CH₃CN and 63% pH2.4 Na₂SO₄/H₃PO₄ mobile phase. FIG. 30 shows that the particles arecapable of encapsulating insulin and releasing it preferentially underhyperglycemic sugar concentrations. FIG. 31 further illustrates thatmore insulin is encapsulated and released as more polymer participatesin crosslinking the particles.

EXAMPLE 10 Plant Lectins

Pisum sativum agglutinin (PSA), a lectin derived from the pea, waschosen as an alternative glucose-binding protein because of its reducedimmunogenicity and mitogenicity. In one embodiment, 0.100 ml of PSA isdissolved at 50 mg/ml in 20 mM BES buffered saline containing 1 mM Mn²⁺,1 mM Ca²⁺, and 1 M NaCl and added to 0.100 ml of a dextran solution thatis dissolved at a known concentration in 20 mM BES buffered salinecontaining 150 mM NaCl. The solutions are allowed to react for one hour,after which the resulting gels are separated from the supernatant. Thegels are washed twice with 1 ml of BES buffered saline solution andfreeze-dried. To evaluate the amount of dextran participating in the gelreaction as a function of dextran molecular weight (MW) and ConA/dextran ratio, the dextrans are fluorescently labeled to easily detecttheir concentration in solution (MW 70 K and 170 K labeled with TRITC,MW 280 K and 500 K labeled with FITC. The fluorescence of each of thesupernatants is measured using a Molecular Devices fmax fluorescencespectrophotometer (TRITC: λ_(ex)=544 nm, λ_(em)=590 nm; FITC: λ_(ex)=485nm, λ_(em)=538 nm), and converted to concentrations using a set ofstandard curves. Crosslinking efficiency (X_(CL)) is calculatedaccording to Equation 1.

EXAMPLE 11 Mammalian Lectins

MBP is dissolved in a pH 7 buffer at 1-100 mg/ml containing 10-100 mMcalcium chloride (CaCl₂). The resulting solution is added to each ofseveral dextran, mannosylated dextran, or yeast mannan solutions ofvarying concentrations. The crosslinking efficiency and glucosesensitivity of the resulting materials are determined as described abovein Example 1. In select syntheses, insulin-dextran,insulin-mannose-dextran, or insulin-mannan conjugates bearing sufficientglucose or mannose residues may be combined with the concentrated MBPsolutions to produce a gel capable of releasing insulin in aglucose-dependent manner. The insulin release may be monitored using theprocedure described in Example 3.

EXAMPLE 12 Conjugation of a Sugar to a Carboxyl Bearing Polymer

12.5 mg of 100% carboxylated CBP is dissolved in 0.625 ml of 0.02 Msodium phosphate buffer, pH 4.5. To this solution, 0.625 ml of a 2%carbodiimide solution is added dropwise and mixed for 4 hours at roomtemperature. The resulting solution is dialyzed against 0.02 M sodiumphosphate buffer, pH 4.5 to remove unreacted carbodiimide and thenagainst a 0.2 M borate buffer, pH 8.5. To the resulting solution,0.5-2.5 mg of mannosamine (MA) or glucosamine (GA) is added and mixedgently overnight at room temperature. 0.050 ml of a 0.25 M ethanolaminesolution is then added to block unreacted sites. The resulting solutionis dialyzed against deionized water and freeze dried to obtainglycosylated-CBP.

EXAMPLE 13 Conjugation of a Sugar to a Carboxyl Bearing Polymer

Sufficient CBP (COOH form) to provide 300 micromoles of carboxylategroups is dried under high vacuum over P₂O₅ and then dissolved in 2 mlof dry dimethylsulfoxide (DMSO). 50 micromoles of tributylamine (TBA)and 50 micromoles of isobutylchloroformate are added at roomtemperature, and mixed under argon atmosphere for 15 minutes. 10-100micromoles of GA or MA are added separately to 3 ml of dry DMSO, thenmixed with the CBP solution, and stirred overnight. The mixtures arethen diluted in three volumes of ice cold water, dialyzed against 0.02%ammonium bicarbonate to remove uncoupled GA or MA, and freeze-dried toobtain dry CBP-GA or CBP-MA conjugates (modified from Baudys, et al.,Bioconjugate Chem., 9, 176-183 (1998), the contents of which areincorporated herein by reference). In select syntheses, the remainingCOOH groups are capped with OH groups by employing the above procedurewith an excess of ethanolamine (EA).

EXAMPLE 14 Covalent Attachment of Insulin to A Biodegradable Polymer

Insulin may be conjugated to CBP as described by Baudys, 1998.Sufficient CBP (COOH form) to provide 300 micromoles of carboxylategroups is dried under high vacuum over P₂O₅ and then dissolved in 2 mlof dry dimethylsulfoxide (DMSO). 50 micromoles of tributylamine (TBA)and 50 micromoles of isobutylchloroformate are added at roomtemperature, and mixed under argon atmosphere for 15 minutes. 25micromoles of insulin are added separately to 3 ml of dry DMSO, thenmixed with the CBP solution, and stirred overnight. The mixtures arethen diluted in three volumes of ice cold water, dialyzed against 0.02%ammonium bicarbonate, and freeze-dried to obtain dry CBP-insulinconjugates. Conjugated insulin is then separated from unconjugatedinsulin using a high-load preparative HPLC size exclusion column (e.g.Superdex 75) and freeze-dried to obtain pure insulin-CBP conjugates.

EXAMPLE 15 Conjugation of a Sugar to an Aminated Scaffold

A method for conjugating sugars to —NH₂ groups is described in Thoma, etal., J. Am. Chem. Soc., 121, 5919-5929 (1999). Briefly, NBP (1 mmolbased on —NH₂ groups) is suspended in a mixture of dimethylformamide(DMF) and 1 ml of 2,6-lutidine under a dry argon atmosphere. At 0° C., asolution of acid anhydride (3.0 mmol) in 1 ml of DMF is added within 15minutes, and the resulting clear solution stirred for 16 hr at 0° C. Theproduct is precipitated by dropwise addition to 40 ml of a stirred 1:1mixture of ethanol and ether. The solid is filtered, washed, and driedunder vacuum. 10.0 mg (0.050 mmol) of dried solid is dissolved in 2 mlof DMF containing 2 equivalents of thioglucose (varying alpha/betaanomer ratio), obtained from Sigma Aldrich. Triethylamine is then addedat 2 equivalents and stirred at room temperature for 16 h. The mixtureis then added dropwise to 30 ml of a 1:1 mixture of ethanol and ether.The precipitate is washed with ethanol and dried under vacuum. The crudeproduct may then be dissolved in deionized water and ultrafilteredexhaustively against fresh deionized water, followed by lyophilizationto produce dry NBP-glucose polymer. The degree of glycosylation iseasily adjusted by varying the equivalents of thioglucose used in thereaction mixture. In this case, the unreacted —NH₂ groups are cappedwith glycerol by adding an excess (3.0 to 5.0 equivalents) ofthioglycerol, obtained from Sigma Aldrich.

EXAMPLE 16 Conjugation of a Sugar to a Hydroxylated Scaffold

OBP may be modified with sugars such as glucose or mannose using thesame DVS procedure used to synthesize mannosylated-dextran. Briefly, OBPis added to a pH 11.4 bicarbonate buffer and activated with DVS.D-mannose or D-glucose is then added and allowed to react for ˜1 hour atroom temperature, after which glycine is added to neutralize and quenchthe reaction. The resulting polymer is dialyzed exhaustively againstdeionized water and finally lyophilized to obtain glycosylated-OBP.

EXAMPLE 17 Conjugation of a Sugar to a Hydroxylated Scaffold

OBP may also be modified with sugars using periodate coupling asdescribed in Mislovicová, et al., Bioconjugate Chem., 13, 136-142(2002), the contents of which are incorporated herein by reference. 100mg of OBP is dissolved in 1-3.5 ml of a 0.05 M aqueous solution ofsodium periodate (NaIO₄) and stirred in the dark at 4° C. for one hour.The volume of periodate solution is varied depending on the degree ofhydroxylation of the OBP and the desired extent of reaction. Thereaction is stopped by adding 1 ml of ethylene glycol and stirring forone hour. The resulting mixture is dialyzed against water andlyophilized. The resulting dry dialdehyde form of OBP is dissolved in 4ml of a 0.05 M phosphate buffer, pH 7 at 10 mg/ml. To this solution, 4ml of a solution of GA or MA in 0.05 M phosphate buffer, pH 7 at 10-50mg/ml is added along with 2.5 ml of a 10 mg/ml sodium cyanoborohydride(NaCNBH₃) solution and the resulting mixture stirred at room temperaturefor 24 hours. The reaction is then stopped by adding a sodiumborohydride (NaBH₄) solution in 0.05 M pH 9.5 borate buffer at aconcentration of 5 mg/ml to reduce the remaining aldehyde groups. Theresulting mixture is stirred for 6 hours at room temperature, afterwhich the pH is adjusted to 7 using 4 M hydrochloric acid (HCl). Theresulting solution is ultrafiltered exhaustively against deionized waterand lyophilized to obtain pure glycosylated-OBP. In this embodiment,equal volumes of the two reactant (polymer and sugar) solutions areemployed to prevent the components from reacting too quickly. The degreeof conjugation is controlled by adjusting the concentrations of thesolutions.

EXAMPLE 18 Conjugation of Insulin to a Hydroxylated Polymer

Insulin may be conjugated to OBP using the same CNBr method that wasused to conjugate insulin to dextran. This conjugation involvesactivating dextran with cyanogen bromide (CNBr) at pH 10 in water,followed by reaction with insulin (L. Kagedal, S. Akerstrom, Acta. Chem.Scand. 25, 1855 (1971)).

EXAMPLE 19 Conjugation of Insulin Secretogues to a Polysaccharide

Kagedal and Akerstrom describe that proteins and peptides containingfree amino groups and also other amino compounds may be coupled todextran by the CNBr method used to conjugate insulin (Kagedal andAkerstrom, 1971). In such a way, the peptides GLP-1 or exanitide may becoupled to dextran or mannosylated dextran, condensed with theappropriate multivalent glucose binding protein such as Con A or MBL,and released from the structure in a glucose-dependent manner to preventadverse hypoglycemia caused by administration of these compounds in anon-glucose-dependent manner.

Sulfonylureas (SU), such as glibenclamide, are conjugated to OBP'saccording to the procedure outlined in S. Kim, et al. Biomaterials. 24,4843 (2003). Briefly, the OBP is dissolved in dimethylsulfoxide (DMSO)with SU and reacted by means of N′,N′-dicyclohexylcarbodiimide (DCC) and4-dimethylaminopyridine (DMAP) as catalysts. The reaction is carried outfor 48 hours under argon and the dicyclohexylurea removed by filtration.The product is precipitated in ethanol, then dissolved in water, andfiltered to remove insoluble particles. Following lyophilization, theproduct is further purified by dialysis, and lyophilized to obtain apure OBP-SU product. In fact, an SU-conjugated pullulan obtained by thisprocedure was shown to possess dose-dependent insulinotropic action (Kimet al., 2003).

EXAMPLE 20 Conjugation of an Antibiotic to a Polysaccharide

Using the Kagedal and Akerstrom CNBr conjugation procedure,antibiotic-dextran conjugates, such as ampicillin-dextran, containingapproximately 300 micromol/g were prepared and found to have significantbacteriostatic capability. Antibiotic-dextran conjugates are thencrosslinked with Con A or any of the other multivalent glucose-bindingproteins described above. The antibiotic-dextran is then released in aglucose-dependent manner to provide long-term, mealtime dosing ofantibiotics with a single administration.

EXAMPLE 21 Conjugation of an Anticancer Drug to a Polysaccharide

A method for conjugating the chemotherapy agent, doxorubicin (DOX) todextran is described in Dillman, et al., Cancer Research, 46, 4886-4891(1986). Briefly, dextran is oxidized with periodate to form apolyaldehyde. The primary amine groups of DOX are reacted with thealdehyde groups on the dextran to form Schiff's bases. This preparationis then reduced with sodium borohydride. The conjugate may be purifiedusing Sephadex G100 gel filtration followed by lyophilization to obtainpurified Dextran-DOX conjugate. Ohya, et al., Biomacromolecules, 2,927-933 (2001) describes a method for conjugating the chemotherapyagent, cisplatin, to dextran. Briefly, a dicarboxymethyl-dextran(DCM-Dex) intermediate is synthesized using diethyl bromomalonate intetrahydrofuran (THF). Cisplatin (CDDP) is precipitated in silvernitrate solution to obtain CDDP (nitrato) and passed through ananion-exchange resin to convert to CDDP (hydroxo). This solution is thenreacted with DCM-Dex solution in water and purified by gel-filtrationover Sephadex G-25 and freeze-dried to obtain purified DCM-Dex/CDDPconjugate. In one embodiment, the anticancer drug-dextran conjugate maybe crosslinked with Con A or any of the other multivalentglucose-binding proteins described above. The anticancer drug-dextran isthen released in a glucose-dependent manner to provide long-term,mealtime dosing of chemotherapy with a single administration.

EXAMPLE 22 Cleavable Therapeutic Agent Conjugates with Polysaccharides

To increase biological activity or decrease plasma residence time, itmay be preferred to release the therapeutic agent from a polymer-agentconjugate. Cleavable polymer-agent conjugates may be synthesized bylinking the therapeutic agent to the polymer backbone through a peptidespacer that can be cleaved rapidly once present in the systemiccirculation. For example, dipeptidyl peptidase IV (DP-IV), atransmembrane glycoprotein, is broadly distributed throughout the bodyand cleaves preferentially Xaa-Pro dipeptides from oligopeptides withlengths <30 amino acids (Engel, et al., PNAS, 100, 5063-5068 (2003)).

Carboxymethyldextran (CMDex) is synthesized according to the procedureof Huynh (Huynh, et al., Die Angewandte Makromolekulare Chemie, 254,61-65 (1998)). Briefly, 2.0 g of dextran are slurried in 42.5 ml oftert-butanol. 7.5 ml of a 3.8 M sodium hydroxide solution is then addedslowly followed by continuous stirring for one hour at room temperature.Then monochloroacetic acid (MCA) is added up to a [MCA]/[Dextran] ratioof 2.5 while stirring to complete homogeneity. After a 90 minutereaction at 60° C., the mixture is cooled, neutralized with acetic acid,precipitated in methanol, filtered, and dried under vacuum.

A Boc-glycyl-glycyl-pro-glycyl (Boc-Gly-Gly-Pro-Gly) may be obtainedcommercially or chemically synthesized using the Merrifield resinprocedure (R. B. Merrifield Science 150, 178 (1965)). In one procedure(M. Harada, et al. J Control Release. 69, 399 (2000)),Boc-Gly-Gly-Pro-Gly is condensed with an amine-containing therapeuticagent (e.g. insulin-NH₂, GLP-1-NH₂, campotothecin-NH₂, doxorubicin-NH₂)in DMF at room temperature in the presence of1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride andtriethylamine. The tert-butoxycarbonyl amide (N-Boc) protecting group isremoved with hydrochloric acid in dioxane in an ice-bath. The resultingdrug-linker is added to CMDex in water in the presence of1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride and reactedbelow 10° C. for two hours at pH 5.5. The resultingDrug-NH-Gly-Pro-Gly-Gly-CMDex conjugate is precipitated in ethanol,filtered, washed, and dried.

In one embodiment, an insulin-NH-Gly-Pro-Gly-Gly-CMDex (Ins-Link-Dex)conjugate is combined with a multivalent glucose-binding proteins toform a gel that degrades to release Ins-Link-Dex in a glucose-dependentmanner. The Ins-Link-Dex is absorbed into systemic circulation where itis rapidly cleaved by DP-IV into free insulin and free CMDex. The freeinsulin then acts on hepatic and adipose tissue with full biologicalactivity and circulation time.

EXAMPLE 23 Scaffold-Engineered Ligand-BindingProteins—Lactate-Responsive Delivery

Other ligand-binding proteins may be synthesized by rationalcomputational design followed by site directed mutagenesis ofligand-binding proteins as described in Looger et al., 2003, thecontents of which are incorporated herein by reference. In one example,a soluble L-Lactate binding protein was synthesized with high affinityand specificity. Modifications to wild-type glucose binding protein(GBP), ribose binding protein (RBP), arabinose-binding protein (ABP),glutamine binding protein (QBP), and histidine binding protein (HBP)produce a binding site that selectively binds L-lactate (FIG. 36). TheL-lactate binding protein is made multivalent by attaching severalprotein molecules to a polymer using the procedures of Example 14 or 18.

Dextran containing lactate oligomers is synthesized according to theprocedure of de Jong (de Jong, et al., Journal of Controlled Release,71, 261-275 (2001)). Briefly, a lactic acid oligomer is synthesized viaring-opening polymerization of lactide with 2-(2-methoxyethoxy)ethanol(MEE) and stannous octoate as initiator and catalyst, respectively.After activation of the hydroxyl end group of the oligomer withN,N′-carbonyldiimidazole (CDI) in tetrahydrofuran (THF) at roomtemperature for four hours, the resulting lactate-Cl is coupled todextran. The coupling is performed at ambient temperature for four daysin dimethylsulfoxide (DMSO) using 4-(N,N-dimethylamino)pyridine (DMAP)as a catalyst.

Dextran-lactate may be condensed with multivalent lactate-bindingprotein to produce a lactate-responsive delivery system. ElevatedL-lactate concentrations are indicative of several medical conditionsincluding extreme muscle fatigue. In one example, a molecule capable ofstimulating expression and/or increasing activity of the monocarboxylatelactate transporter (Halestrap, et al., Biochem. J, 343, 281-299 (1999))is encapsulated in dextran-lactate cross-linked with multivalentlactate-binding protein. The molecule is then released in a L-lactatedependent fashion to remove rapidly remove the metabolite fromcirculation.

EXAMPLE 24 Production of N-desulfated N-acetylated Heparin

One gram of heparin is dissolved in 30 ml water and applied to a columnof [BIO-RAD AG50 W=X8 (H⁺)] resin. The pass-through fraction eluted withwater is neutralized immediately with pyridine and dialyzed overnightwith distilled water at 4° C. This is lyophilized to obtain 1.0 g ofheparin pyridinium salt. Complete N-desulfation of 500 mg of the salt isachieved through solvolysis as described by Danishefsky, “Methods inCarbohydrate Chemistry”, Vol V, 1980, pp407-409, the contents of whichare incorporated herein by reference, and Nagasawa, “Methods inCarbohydrate Chemistry,”, Vol. VIII, 1980, pp291-294, the contents ofwhich are incorporated herein by reference. N-acetylation of thede-N-sulfated heparin is performed according to Danishefsky (1980)(Sugahara, 2001).

EXAMPLE 25 Production of Carboxymethylated Dextran

Two grams of DexT10 (Extrasynthese Co.) is dissolved in 40 ml of water.6.8 g of NaOH is added and the mixture chilled on ice. After adding 9.4g of chloracetic acid, the mixture is stirred at room temperature for 20h to obtain the sodium salt of CMDex (Sugahara, 2001).

EXAMPLE 26 Production of Carboxymethylated Dextran

Dextran having a molecular weight between 10,000 and 40,000 is dissolvedin tert-butanol, isopropanol, 1,1,3,3 tetramethylurea, or a mixture ofDMSO and tetramethylurea. Sodium hydroxide solution of a concentrationin the 2M-8M range is added slowly and stirred for 1 hour at roomtemperature. Where a solvent other than tert-butanol is used, thesolvent/water ratio is about 85:15. Monochloroacetic acid is added until[MCA]/[dextran] is in the range of 1-3.5 while stirring to maintainhomogeneity. The mixture is maintained at 60° C. for up to 240 mins. Themixture is then cooled to room temperature and neutralized with glacialacetic acid. The chloromethylated product is then precipitated withmethanol (Huynh, 1998).

EXAMPLE 27 Production of a Galactose Responsive Drug Delivery System

Galactosamine is linked to a CBP using the techniques of Examples 12 or13, or galactose is linked to an OBP using the techniques of Example 18.The recombinant galactose-binding lectin subunit developed byMedina-Bolivar et al., Vaccine 21, 997 (2003), the contents of which areincorporated by reference, is attached to a biodegradable polymer toform a polyfunctional lectin. The polyfunctional lectin and thegalactosylated polymer are mixed in the presence of galactosetransferase to form a gel. The gel may be used to treat galactosemia. Anincrease in the galactose concentration in serum will cause the gel todegrade and release the enzyme. Other galactose-specific lectins includericin, mistletoe galactose-binding lectin ML-1, and abrin. Thegalactose-binding subunit should be purified from the toxic subunitsbefore incorporation into a gel for use with the invention.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

1. A material for delivery of a therapeutic agent in response to anindicator, comprising: conjugates that include a therapeutic agentcovalently linked to a polymer, wherein the polymer includes two or moreindicator analogs; and polyfunctional cross-linking agents thatcross-link conjugates by non-covalently interacting with indicatoranalogs on different conjugates, wherein: the material is insoluble inthe absence of an indicator that competes with the indicator analogs fornon-covalent interactions with the cross-linking agents; conjugates arereleased from the material in the presence of the indicator at a ratethat varies within physiological concentrations of the indicator; theindicator is glucose; the indicator analogs comprise glucose and/ormannose residues; and the therapeutic agent is insulin or an insulinsecretogue.
 2. The material of claim 1 wherein the polyfunctionalcross-linking agents are covalently linked to the polymer.
 3. Thematerial of claim 1 wherein the material is comprised of a plurality ofparticles.
 4. The material of claim 3 wherein the particles have a sizefrom about 100 nm to about 300 nm.
 5. The material of claim 3 whereinthe particles have a size from about 300 nm to about 500 nm.
 6. Thematerial of claim 3 wherein the particles have a size from about 500 nmto about 5 μm.
 7. The material of claim 3 wherein the particles have asize from about 5 μm to about 50 μm.
 8. The material of claim 3 whereinthe particles have a size from about 50 μm to about 100 μm.
 9. Thematerial of claim 1 wherein the therapeutic agent is covalently linkedto the polymer by a bond that is susceptible to enzymatic cleavage. 10.The material of claim 1 wherein the indicator analog is a portion of aside group of the polymer.
 11. The material of claim 1 wherein thepolymer is derivatized with the indicator or the indicator analog. 12.The material of claim 1 wherein the indicator analog is incorporatedinto the backbone of the polymer chain.
 13. The material of claim 1wherein the polymer is selected from poly(lactic acid) (PLA),poly(glycolic acid) (PGA), PLA-PGA co-polymers (PLGA), poly(anhydrides),poly(hydroxy acids), poly(ortho esters), poly(propylfumerates),poly(caprolactones), polyamides, polyamino acids, polyacetals,biodegradable polycyanoacrylates, biodegradable polyurethanes,polysaccharides, co-polymers of the above, adducts of the above, andmixtures of the above.
 14. The material of claim 1 wherein the polymeris selected from carboxylated polysaccharides, —NH2 pendantpolysaccharides, hydroxylated polysaccharides, alginate,collagen-glycosaminoglycan, collagen, dextran, pullulan, mannan,amylose, amylopectin, glycogen, cellulose, hyaluronate, chondroitin,dextrin, chitosan, co-polymers of aminated and non-aminated amino acids,co-polymers of hydroxylated and non-hydroxylated amino acids,co-polymers of carboxylated and non-carboxylated amino acids,co-polymers of the above, adducts of the above, and mixtures of theabove.
 15. The material of claim 1 wherein the polyfunctionalcross-linking agents include a protein selected fromphytohemoagglutinins, human mannan binding protein (MBP), humanpulmonary surfactant protein A (SP-A), human pulmonary surfactantprotein D, CL-43 and conglutinin.
 16. The material of claim 15 whereinthe phytohemoagglutinin is selected from concanavalin A (Con A) andphytohemoagglutinins derived from pisum sativum (pea), lathyrus odoratus(sweet pea), lens culinaris (lentil), narcissus pseudonarcissus(daffodil), vicia faba (fava bean), and vicia sativa (garden vetch). 17.The material of claim 1 wherein the polyfunctional cross-linking agentsinclude a polyfunctional binding protein.
 18. The material of claim 1wherein the polyfunctional cross-linking agents include a plurality ofmonofunctional binding proteins or binding fragments of proteins linkedto one another.
 19. The material of claim 18 wherein the polyfunctionalcross-linking agents include a plurality of monofunctional bindingproteins or binding fragments of proteins covalently attached to apolymer.
 20. The material of claim 1 further comprising a fluorophore.21. The material of claim 20 wherein the fluorophore is covalently ornon-covalently linked to the polymer, the therapeutic agent, or apolyfunctional cross-linking agent.
 22. The material of claim 1 whereinthe polymer is a polysaccharide and the polyfunctional cross-linkingagents include a plant lectin or a mammalian analog to a plant lectin.23. The material of claim 1 wherein the polymer is dextran ormannose-derivatized dextran, the polyfunctional cross-linking agentsinclude concanavalin A, and the therapeutic agent is insulin.
 24. Thematerial of claim 1 wherein the polyfunctional cross-linking agents arenot covalently linked to the polymer.
 25. The material of claim 24wherein the polymer is a polysaccharide, the polyfunctionalcross-linking agents include a lectin, and the therapeutic agent isinsulin.
 26. The material of claim 1 wherein the polyfunctionalcross-linking agents include concanavalin A.
 27. The material of claim 1wherein the polyfunctional cross-linking agents include a chemicallymodified concanavalin A.
 28. The material of claim 1 wherein thepolyfunctional cross-linking agents include a pegylated concanavalin A.29. The material of claim 1 wherein the therapeutic agent is insulin 30.The material of claim 1 wherein the therapeutic agent is an insulinsecretogue.
 31. The material of claim 30 wherein the insulin secretogueis a sulfonylurea.
 32. The material of claim 31 wherein the sulfonylureais glibenclamide.
 33. The material of claim 30 wherein the insulinsecretogue is GLP-1 or a GLP-1 analogue.
 34. The material of claim 33wherein the GLP-1 analogue is exanitide.
 35. The material of claim 1wherein the indicator analog includes glucosamine or mannosamine. 36.The material of claim 1 wherein the polyfunctional cross-linking agentsbind glucose and mannose.
 37. A method comprising administering amaterial of claim 1 to a patient.
 38. The method of claim 37 wherein thematerial is administered by subcutaneous injection.
 39. The method ofclaim 37 wherein the polyfunctional cross-linking agents includeconcanavalin A.
 40. The method of claim 37 wherein the polyfunctionalcross-linking agents include a chemically modified concanavalin A. 41.The method of claim 37 wherein the polyfunctional cross-linking agentsinclude a pegylated concanavalin A.
 42. The method of claim 37 whereinthe therapeutic agent is insulin
 43. The method of claim 37 wherein thetherapeutic agent is an insulin secretogue.
 44. The method of claim 43wherein the insulin secretogue is a sulfonylurea.
 45. The method ofclaim 44 wherein the sulfonylurea is glibenclamide.
 46. The method ofclaim 37 wherein the insulin secretogue is GLP-1 or a GLP-1 analogue.47. The method of claim 46 wherein the GLP-1 analogue is exanitide. 48.The method of claim 37 wherein the indicator analog includes glucosamineor mannosamine.
 49. The method of claim 37 wherein the polyfunctionalcross-linking agents bind glucose and mannose.